This invention relates to wireless communications systems and, more particularly, to wireless communications between wireless terminals and base stations.
In wireless communications systems, wireless terminals (WTs) are paged, i.e., have special messagesxe2x80x94so-called paging messagesxe2x80x94sent to them, by associated base stations (BSs) to initiate communications. In order to realize this, the base stations typically have a channel on the downlink called the paging channel. In prior known paging arrangements, the paging channel is subdivided into a plurality of paging time slots. A group of wireless terminals is typically allocated a paging time slot of a prescribed periodicity for receiving paging messages from associated base stations. As shown in FIG. 1, wireless terminals 1 to N are allocated to time slot 1, wireless terminals N+1 to Y are allocated to time slot 2, and so on. Each wireless terminal is expected to monitor for paging messages from an associated base station during these paging time slots. To this end, the periodicity of the paging time slots is made sufficiently long that each of the wireless terminals can effectively turn off most of its circuitry between two of its designated paging time slots and, thus, save energy. This is referred to as the wireless terminal entering a so-called xe2x80x9csleepxe2x80x9d mode. The wireless terminal, even though in the sleep mode, still has to keep track of the received paging time slots. The wireless terminal is caused to xe2x80x9cwake upxe2x80x9d prior to the arrival of its designated paging time slot, tunes to the downlink channel, and achieves carrier, timer and frame synchronization. Then, the wireless terminal decodes the paging time slot, and if its identifier is included in the wireless terminal""s designated paging time slot, it knows that the paging message is meant for it. The wireless terminal then takes the appropriate action indicated in the paging message. If the paging message is not meant for the wireless terminal, it returns to the sleep mode, and monitors the next received paging time slot designated for it.
A disadvantage of this prior paging arrangement is that the wireless terminal has to decode the entire paging message in order to determine if the message is meant for it. When many wireless terminals share the paging time slot, it is quite likely that the paging message is not meant for that particular wireless terminal. This can cause the wireless terminal to expend power and reduce its battery life unnecessarily.
Problems and limitations of prior wireless paging arrangements are overcome by employing a unique paging time slot format. In the unique paging time slot format, each of the allocated paging time slots occurs periodically and is split into several prescribed paging time slots including at least one first type paging time slot having a relatively short duration and at least one second type paging time slot having a longer duration. The at least one first type paging time slots is of relatively short duration and transports an indication whether a particular associated wireless terminal was paged. The second type paging time slot is of longer duration than the first type time slot and transports the entire paging message.
Specifically, a wireless terminal that is normally in a standby mode only has to enter a monitor mode, i.e., xe2x80x9cwake upxe2x80x9d, to monitor the relatively short first type paging time slot to determine whether it has been paged. If it has been paged, the wireless terminal then monitors the longer second type paging time slot to determine if it is transporting a valid paging message for the paged wireless terminal. If no valid paged indication is detected in the first type paging time slot or no valid paging message is detected in the second type paging time slot, the wireless terminal returns to the standby mode, i.e., returns to a xe2x80x9csleepxe2x80x9d state, and waits for the next periodic occurrence of its assigned paging time slot.
A technical advantage of this unique two type time slot format is that only a small number of bits need to be decoded by the wireless terminal from its designated first type time slot to determine if the paging message in the second type time slot is meant for it. As a result, the wireless terminal does not have to perform as much xe2x80x9cworkxe2x80x9d for paging messages not intended for it, and consequently conserves power and extends battery life.